1. Field of the Invention
The invention relates to a method and an arrangement for controlling the data stream in a vibration-resistant playback device.
2. Related Art
Particularly in the mobile use of playback devices of optical or other information media, vibration-resistant properties are required in order to ensure uninterrupted reproduction of information despite vibrations which lead to interruptions in the reading of data from the information medium.
In order to achieve a vibration-resistant behaviour, the data are written to a buffer memory at a rate which is higher than normal and are read out at the normal rate. If vibrations cause an interruption in the reading of data from the information medium, then this gap in the source data stream can be bridged by reading out the data reserve in the buffer memory which has been stored as a precaution in the meantime.
A method and an apparatur for reproducing data from a disk medium at a variable data rate and for converting the reproduced data to a constant data rate, already have been described in GB 2289158. The apparatus comprises: a reproducing head for reproducing the data from the disk medium at the variable data rate; buffer memory means for storing the reproduced data from the reproducing head and for reading out the stored data at a constant data rate; means for detecting overload of the buffer memory means; and servo means responsive to the overload detecting means for controlling the reproducing head to repeat reproduction of data from the disk medium when overload of the buffer memory means has been detected and the method comprises: storing in a buffer memory data reproduced form the disk medium by a reproducing head at a variable data rate; reading out the stored data from the buffer memory at a constant data rate; detecting overload of the buffer memory; and controlling the reproducing head to repeat reproduction of data from the disk medium when overload of the buffer memory has been detected.
In most of the commercially available devices, the reading of data from the information medium is realized at a doubled rate. However, during operation free from vibrations, this constantly leads to an overflow of the buffer memory, thereby necessitating artificial interruptions in the reading of data from the information medium or returns.
The always doubled rate and the jumps of the scanner cause an increased current consumption. In order to eliminate this disadvantage, it has already been proposed to carry out the reading of data from the information medium with a variable rate. In order not to have to perform the obligatory error checking and possible error correction and/or masking on a source data stream with a variable rate, in accordance with the proposal the requisite processing stages for these measures were connected downstream of the buffer memory. However, this requires an increased storage capacity or, with the existing storage capacity, reduces the useful data that can be stored since, after all, the check data have to be concomitantly stored as well as the useful data.